1. Field of the Invention
This invention relates to a semiconductor device where a p-channel Metal Insulator Semiconductor (MIS) transistor and an n-channel MIS transistor each of which has a metal gate have been formed on the same substrate.
2. Description of the Related Art
Recently, attention has been focused on the metal gate techniques for using metal as gate electrode materials in a complementary MIS (CMIS) device where a p-channel MIS transistor and an n-channel MIS transistor are formed on the same substrate. Since metal has as high a charge density as an atom density, when metal is used as a gate electrode, the depletion of the gate electrode can be ignored.
In a CMIS device using a metal gate electrode, a so-called dual-metal-gate CMIS structure is needed to realize a low threshold voltage. To form a dual-metal-gate CMIS structure, the gate electrode of each of the n-channel MIS transistor and p-channel MIS transistor is needed to have an effective work function close to the conduction band end and valence band end of Si. Specifically, the effective work function of the gate electrode of the p-channel MIS transistor is required to be 0.4 eV or more higher than the effective work function of the n-channel MIS transistor. At present, a general method of realizing this is to configure the gate electrode of the n-channel MIS transistor and that of the p-channel MIS transistor using completely different metal materials (e.g., refer to JP-A 2004-207481 (KOKAI) and U.S. Pat. No. 7,030,430).
However, when different metal materials are used for the gate electrode of the n-channel MIS transistor and that of the p-channel MIS transistor, the n-channel MIS transistor and p-channel MIS transistor have to be dealt with separately in forming and processing their gate electrodes. This makes the manufacturing processes complex and causes the problem of increasing the manufacturing cost. In the method disclosed in JP-A 2004-207481 (KOKAI), the work function of each gate electrode is made different by using molybdenum as gate electrode material for the p-channel MIS transistor and n-channel MIS transistor and at the same time introducing carbon into one of them. In this case, the manufacturing process is complicated.
To realize the introduction of metal gate techniques, it is necessary to find such a dual-metal-gate CMIS structure as prevents the manufacturing processes from becoming complicated as much as possible.
As described above, the introduction of dual-metal-gate techniques is indispensable for improving the performance of CMIS devices. To realize this, it is necessary to cause the metal material for the gate electrode of the n-channel MIS transistor to differ from that for the gate electrode of the p-channel MIS transistor, which is the factor that makes the manufacturing processes complex and increases the manufacturing cost.